An image projector that forms an optical image (projection optical image) by driving light valves, irradiated by illuminating light, based on image signals, and projects an enlargement of this optical image onto a screen, is conventionally known as a means to display a large image.
Japanese Laid-Open Patent Application Sho 62-180343, for example, discloses a reflective image projector having a spectro-optical system comprising a dichroic mirror, a total reflection mirror, and three liquid crystal light valves that form optical images of R, G and B components behind the projection optical system. Illuminating light is led to the liquid crystal light valves from the projection optical system via the spectro-optical system and the reflection of the illuminating light off of the liquid crystal light valves (optical images) is projected onto a screen in front of the projection optical system via the spectro-optical system and the projection optical system. A plate-like total reflection mirror is located at the aperture position of the projection optical system such that the illuminating light from the light source, irradiated from a direction perpendicular to the optical axis of the projection optical system, will be totally reflected by the total reflection mirror so as to (i) pass through half of the effective light pass-through area of the aperture in a direction parallel to the optical axis of the projection optical system and (ii) irradiate the liquid crystal light valves.
Japanese Laid-Open Patent Application Hei 7-159722 discloses a reflective image projector in which a light path splitting surface is located on the path of the illuminating light from the light source, and the light beams, reflected off of the light valves into the illuminating light path and comprising optical images, are split by the light path splitting surface into light beams that run in a direction perpendicular to the illuminating light and are projected onto the screen via reflection. The light beams from the light source are divided into multiple secondary light sources by means of fly eye lenses and these light beams from the secondary light sources irradiate the panel surfaces of the light valves, in a parallel fashion, through a relay lens, such that the illuminance distribution on the panel surfaces is made uniform.
Japanese Laid-Open Patent Application Hei 8-271854 discloses a reflective image projector having (i) an image forming lens, a deflective beam splitter and a dichroic prism located in the path of the illuminating light from the light source; (ii) a liquid crystal light valve located on each of the three exit surfaces of the dichroic prism; and (iii) a projection optical system located on the side of the exit surface of the polarized beam splitter, which is perpendicular to the light path of the illuminating light, wherein a kaleidoscope is located between the light source and the image forming lens.
The image projector disclosed in the Japanese Laid-Open Patent Application Sho 62-180343 converges the illuminating light from the light source to the aperture position of the projection optical system by means of a relay lens and reflects the secondary light source images toward the liquid crystal light valves by means of a total reflection mirror. Consequently, it is difficult to make the illuminance distribution on the liquid crystal light valve panel surfaces sufficiently uniform and to reduce the unevenness in the brightness of the projected image.
The image projector disclosed in Japanese Laid-Open Patent Application Hei 7-159722 splits the light source into multiple secondary light sources using multiple fly eye lenses in order to make the illuminance distribution on the light valve panel surfaces uniform. However, since it has a construction in which the multiple fly eye lenses are placed in a step configuration, the construction of the fly eye lenses is complex and is disadvantageous in terms of cost as well.
The image projector disclosed in the Japanese Laid-Open Patent Application Hei 8-271854 has a construction wherein the light source and the liquid crystal light valves are arranged linearly, and the illuminating light and the projection light are separated by means of a polarized beam splitter located on the path of the illuminating light from the light source. Consequently, the projection optical system increases in size, making it difficult to make the image projector compact.
The present invention was conceived in view of these problems. It provides an image projector having a compact construction, in which the illuminance distribution on the light valve panel surfaces is made uniform and the unevenness in the brightness of the projected image is reduced.